The present invention broadly relates to the measurement of fluid flow. It particularly relates to a device for ensuring the accuracy and reliability of fluid flow measurements taken from a pitot tube with a pressure-sensing means. When pitot tubes are employed in connection with pressure measuring devices for determining the flow of fluids, either liquids or gases, they frequently can become clogged with foreign matter which lodges in the openings or orifices in the tubes. This clogging results in erroneous or erratic readings and may necessitate ceasing operations for a sufficient time to permit the removal and cleaning of the tubes. Various devices have been suggested to overcome this problem.
In U.S. Pat. No. 1,438,811 there is disclosed a device which permits the examination, removal and cleaning of a pitot tube without the necessity of cutting off the passage of fluids passing through the conduit in which the pitot tube is located. Broadly, the device comprises a bushing extending through one side of the conduit and adapted to removably receive the pitot tube. A sleeve extends through the opposite side of the duct and is adjustable toward or away from the bushing. The device further includes means for closing the outer end of the sleeve when it is separated from the bushing, the means being adapted to being opened when the sleeve is in contact with the bushing. While the device disclosed performs its intended function, it obviously requires considerable time and manual steps to perform the cleaning operation.
U.S. Pat. No. 2,488,810 discloses an automatic shutter mechanism for covering the opening in a pitot tube for use on an aircraft. The device includes a shutter which is biased by a spring to cover the opening to the tube. It further includes a pressure plane which is acted upon by air during flight of the aircraft to withdraw the shutter and uncover the opening in the pitot tube by overcoming the spring force.
U.S. Pat. No. 2,532,316 discloses an automatically releasable cover for aircraft pitot tubes. The device comprises a fabric cover which encloses the free end of the pitot tube, a latching means for retaining the cover in position, and an air pressure responsive means adapted to automatically release the latching means upon forward movement of the aircraft after it has reached some predetermined rate of speed.
U.S. Pat. No. 3,380,298 describes a device for purging a pitot tube. The device comprises a three-way valve connected to a static side of the pitot tube, the static side of a manometer, and a supply of gas under pressure. A second three-way valve is connected to the velocity pressure side of the pitot tube, the velocity pressure side of the manometer and the supply of gas under pressure. A third valve is provided to connect the two three-way valves and cut off both of those valves from the supply of pressurized gas and open them to the atmosphere to exhaust pressurized gas therefrom. There further is disclosed a means for operating all the valves in appropriate sequence.
U.S. Pat. No. 3,638,490 describes another fluid flow measuring device. The device includes means for determining the velocity and depth of a flowing body of fluid such as fluid flowing in a water or sewer main. The means includes a conduit immersed in the flowing fluid, means for forcing gas out through the immersed conduit into the flowing fluid and other means responsive to the force or pressure required to force gas into the flowing fluid. The means responsive to the force or pressure is calibrated to indicate information from which the depth or velocity of the fluid body can be determined.